Download Carbonate Rock Formation

Carbonate Rock Formation
Limestone, dolomite (or dolostone), and marble
are often collectively referred to as carbonate
rocks because the main mineral is calcite. The
chemical name of calcite is calcium carbonate.
Limestone, dolomite, sandstone and shale are
sedimentary rocks (there are also other
sedimentary rocks) that are often found
together in a rock group .
Carbonate Rock Formation
Sedimentary rocks are formed from small pieces
of other things that pile up together and then
get compacted into a rock.
Sandstone for example is formed when granite
rock erodes releasing small grains of quartz
(sand). When the sand piles up and gets
compacted sandstone is formed.
Limestone is formed when sea shells (snails,
clams, etc.) are dissolved chemically and then
deposited (piled up) and compacted.
Carbonate Rock Formation
Sedimentary rocks OFTEN but not always have
fossils in them.
If there are fossils the identification of the rock
and the age of the rock is easier to determine.
The only natural process that we know of to
produce limestone and shale occur in water
(ocean) environments.
Sandstone can be produced in a desert and wind
environment but is more commonly produced
in a water environment.
Carbonate Rock Formation
The stuff settling out of water at any one time
depends on two factors:
1. The speed of the water motion
2. The size (mass) of the particles.
The faster the water moves, the bigger the
particles it can carry.
When a river is flowing it is often carrying a
mixture of mud, sand and other small particles.
Carbonate Rock Formation
When the river flows into a large lake or ocean
the biggest particles will settle out first and the
smallest last.
This means that sand piles up near the shore
where it can settle out first.
Mud will pile up a little further out into the
ocean because it settles out more slowly.
Calcite (the main mineral in limestone) will pile
up further out into the ocean, in clear water
areas where shelled animals can live.
Carbonate Rock Formation
The diagram at the left shows the general
layering of the sedimentary rocks in south
eastern Minnesota.
Notice the combined pattern of limestone,
sandstone and shale. Pay attention to the
symbols used to represent each type of rock.
The oldest rock is at the bottom because it
was put there first, the youngest rock is at
the top.
Why are there different layers?
What happened to cause each of the layers?
You have this diagram in the Caves in
Minnesota publication from the Minnesota
Geological Survey
Carbonate Rock Formation
Sedimentary rocks are put in place in nearly
horizontal layers with the oldest at the bottom.
Sandstone is formed near sea shores
Mudstone and shale is formed further out to sea
Limestone is formed even further out to sea
What does the evidence of variable layers on the
bedrock tell us about this area?
Notice that Hutchinson is very near the border of
the limestone bedrock on the maps from the
Minnesota Geological Survey.
Carbonate Rock Formation
Ancient tropical seas from the Minnesota
Geological Survey describes the process of the
sedimentary rock formation in southeastern
Minnesota during Cambrian and Ordovician
times.
Study the diagrams carefully.
Note how the different sea levels left behind
different types of rocks.
Again, notice the location of Hutchinson in
comparison to the types of bedrock.
Carbonate Rock Formation
The time scale for this rock formation along with
other rocks in Minnesota is outlined in
Precambrian Geology from the Minnesota
Geological Survey
We will be considering geologic time in much
more detail in a later unit so you will not be
responsible for knowing this time scale now
but it is a good introduction that will be
reinforced each unit through the end of the
trimester.
How Do We Know?
A reasonable question. Where is the evidence for
all of this.
First, the evidence is complicated and obscure. In
most places it is not in places where we can
see it.
The evidence has increased greatly in the last
few years with the combination with gps,
Geographic Information Systems (GIS)
databases and drill core or water well records
Evidence
Every well or core sample drilled in Minnesota
must be logged and stored. As this information
is analyzed the picture of the bedrock in
Minnesota has become more clear.
In 2008 additional evidence was collected in
McLeod county as the Minnesota Geological
Survey did additional drilling, sampling and
collecting to learn more about our bedrock as
well as our glacial drift.
Evidence
As more evidence is collected we have more
pieces that fill in the details of the story of
Minnesota and the earth.
Carbonate Rock Formation
•  http://www.pca.state.mn.us/water/
groundwater/karst.html